Count the number of dimension of an object of thought. The lower the number of dimensions the more strongly it relates to an introvert perceiving function. The higher the number, the more strongly it relates to an extrovert perceiving function.
The strict way of putting it is that all things that Pi deals with are 1-dimensional. 1-dimensional things are simply sequences.
A chair is a 3-dimensional object. Very Pe.
It can get worse though. A thought space of possible configurations of attributes of a chair (a color gradient, a height scale, etc) can be anything up to even 7-dimensional. Pe to the max.
A film is... a 1-dimensional sequence of 2-dimensional pictures. A mixture of Pi and Pe. Pretty close to Pi, but also processable as Pe when taken in as a whole.
A historical time-line is a 1-dimensional sequence of events. Fully Pi.
A verbal sentence is a sequence of words. 1 dimensional. Pi.